1. Field of the Invention
The present invention relates to an oxygen concentration system, especially of the OBOGS type, for aircraft, in particular for long-range, large-capacity airliners.
2. Related Art
At the present time, gaseous oxygen is used by the pilots and passengers of a civil commercial airliner in the event of cabin decompression (passengers and pilots), in the event of protection against smoke and toxic gases (pilots) and in the event of prior protection when cruising at high altitude (pilots).
Moreover, the pilots of military aircraft have need for a permanent oxygen supply, throughout their flight missions. In certain specific missions, the same applies to the crew of military tactical transport planes and helicopters.
The constraints imposed by the aeronautical environment mean equipment must be designed to be as light as possible and capable of providing the largest quantity of oxygen possible, with substantial self-sufficiency, and consequently the least possible logistics.
In modern fighter planes, the pilot or pilots are permanently supplied by an on-board oxygen generating system (commonly abbreviated to OBOGS), using the technology for separating gases from the air by a zeolite-type molecular sieve.
Document EP-A-391 607 thus discloses an OBOGS-type oxygen concentration system that can be used for supplying the crew members of an aircraft using an adsorbent of the molecular sieve type.
Furthermore, document U.S. Pat. No. 4,960,119 also teaches an OBOGS-type system using adsorbents that have a higher affinity for nitrogen than for oxygen.
Moreover, other OBOGS-type systems are also disclosed by documents U.S. Pat. No. 4,651,728 and EP-A-0 364 283.
On the other hand, in civil aircraft, the total supply of gaseous oxygen to the people on board is provided by pressurized oxygen cylinders or by chemical oxygen generators, for example on the AIRBUS A340 (tank of oxygen in gaseous form) and AIRBUS A320 (chemical generator). These civil oxygen production systems are currently designed and sized so as to deliver oxygen to the passengers for a period varying from 15 to 22 minutes, essentially following a loss of cabin pressure.
As in the case of military aircraft, it is now envisaged to also equip new airliners, especially long-range, large-capacity airliners, for example the AIRBUS A380-type planes, as well as business planes, with on-board systems of the OBOGS type based on an adsorbent molecular sieve.
This is because, compared with oxygen storage, molecular-sieve OBOGS-type systems have the advantages:                of a weight saving when the time they are in use typically exceeds 30 min, as is the case with the planned diverting of aircraft to the new longer-haul air routes;        of reduced logistics;        of greater safety and availability; and        of unlimited self-sufficiency.        
These same advantages also exist when the OBOGS system is on board a military tactical transport plane or a helicopter, when these have to carry out missions requiring the use of oxygen.
However, one problem that arises is that the existing OBOGS-type systems are much heavier than conventional on-board oxygen storage systems, and this constitutes a serious impediment to their use in aircraft in which the reduction in on-board weight is a constant concern, as it has a not insignificant impact on fuel consumption.
In other words, the problem that arises is to be able to fit molecular-sieve OBOGS-type systems on board aircraft without this having a negative impact on the on-board weight, and to achieve this with substantially the same, or even greater, oxygen production compared with a conventional system.